The present invention relates to a machine for packaging a commodity as placed in a tray with a plastic film material. More specifically, the invention relates to a packaging machine designed so that trays are arranged at predetermined spaced intervals in a continuous tube formed of a belt-like film of a relatively easily stretchable thermoplastic resin material while such tube is being formed, the tube is cut between each two successive trays, and then the both ends of each cut tube are folded on to the bottom of the tray enclosed therein while being stretched. The invention provides a packaging machine of the tube forming type which permits covering up each tray with a film material in a satisfactorily taut condition.
Known as basic packaging machines of such type are those disclosed by U.S. Pat. Nos. 3,973,372 and 4,144,697. Without exception, these machines are very large in size so that purchase and use of any such machine require considerable cost. From the standpoint of people who manufacture and sell such machines, it is almost impossible to expect the economic burden of the user could be reduced, unless improvements directed toward simplified construction without any decrease in packaging efficiency permits manufacture and sale at economical cost. Without such improvement, favorable commercial operation cannot be expected either.
The prior-art packaging machines as disclosed in the above cited U.S. Patents include means for forming belt-like film into tube forming means, means for feeding trays on to the tube forming means, cutting means for cutting a film tube so formed at points before and behind each tray, vacuum pump means for pulling both ends of each cut tube downwardly, means for folding the cut end of each tube cut on the rear side of the tray on to the bottom of the tray, and means for folding the cut end of each tube cut on the front side of the tray on to the bottom of the tray. One particular disadvantage of the prior-art packaging machines is that the cut tube end on the front side of the tray cannot be folded earlier than the cut tube end on the rear side. The direction the cut tube end is folded on the front side of the tray is opposite to the direction in which the rear side is folded. Therefore if the cut tube end on the front side of the tray is folded at an earlier moment, the folded rear side may come out of contact with the bottom of the tray under the influence of movement of the open-hole rotor means when the tray passes over the rotor means. For this reason, means for folding the cut tube end on the front side of the tray are provided after folding the rear side. Moreover, since the length of the tray to be used varies depending upon the packaging operator's choice, the distance between the first air suction port in the vacuum pump, for pulling downward the cut tube end on the rear side of the tray, and the second air suction port, for pulling downward the cut tube end on the front side of the tray, is required to be set so as to meet the maximum size requirement for trays to be used. This has been a factor responsible for the prior art machines being very large in size. Another disadvantage of conventional machines is that rotary cutting means used therein are relatively complicated in construction, particularly as to bearings for vertically opposed rotors and gear arrangement for synchronous rotation of the rotors.